Sublimed oxide furnace



Nov. l, 1960 J. M. NoY ETA.

SUBLIME@ oxrDE FURNACE 5 Sheets-Sheet 1 Filed June 20, 1958 NNnmL Nov.1, 1960 J. M. NoY ETA. 2,958,588

SUBLIMED OXIDE FURNACE Filed June 20, 1958 5 Sheets-Sheet 2 ,f i@ ",f j

Nov. 1, 1960 J. M. NoY ETAL 2,958,588

SUBLIMED oxIDE FURNACE Filed June 2o, 1958 5 Sheets-Sheet 3 INVENTORS.

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Nov. 1, 1960 J. M. NoY ETAL SUBLIMED oxInE FURNACE 5 Sheets-Sheet 4Filed June 20, 1958 1N VEN TORS Nov.. l, 1960 J. M. Nov Erm. 2,958,588

SUBLIMED OXIDE FURNACE Filed June 20, 1958 5 Sheets-Sheet 5 INVENTORS,J2e/ may ,.ger C 677:2???

United States Patent SUBLIMED OXIDE FURNACE VJack M. Noy, Sorel, Quebec,Canada, and Delbert C.

Filed June 20, 1958, Ser. No. 743,282

8 Claims. (Cl. 2'3264) This invention relates generally to furnaces andmore particularly to a furnace :for producing molybdenum trioxide(M003), sometimes called molybdic anhydride or molybdic acid, andcommonly referred to in the molybdenum processing held as oxide, bysubliming a high pur-ity molybdenum trioxide fnom a lower pur-ity leedmaterial.

YPrior furnaces for obtaining high purity oxide (better than 99% M003)from technical grade oxide (approximately 90% M003 .and containing someM002 and insoluble impunities such as aluminum oxide, silica and ironoxide) have utilized a. rotating hearth located below the furnaceheating units. Technical grade oxide, continuously fed to the hearthwhich is heated by radiant heaters to approximately 2100 degreesFahrenheit, starts volatilizin-g at about 1100 degrees Fahrenheit whichis approximately 300 degrees below its melting point. streams passedover different sections of the hearth sweep the sublimed oxide out ofthe furnace to be cooled, collected, densiied and placed in containersat the baghouse. `One of the principal problems in 'furnaces of thistype has been that since uniform conditions do not exist at all sectionsof the hearth, it has been diicult to obtain oxide of uniform purity[from all of the hearth sections. It the stream at a hearth section istoo large, it picks up impurities from the oxide on the hearth so thatthe resulting oxide is below the required purity, and cools the oxide onthe hearth to an extent such that the production rate is lowered. It the:air stream is too small, the oxide bed on the hearth becomes molten,rather than remaining in the desired sticky non-ilowable mass, and therate at which oxide is removed from the hearth section is reduced sothat the output of the furnace is lowered. In la furnace having vabustle type of air exhaust pipe, namely, an exhaust pipe which extendsaround the furnace and communicates at spaced points along its lengthwith the furnace hearth :and is connected at one of its ends to asuctiondevi-ce, when the dampers at the spaced points are adjusted so that thesuction pressures at the spaced points of the hearth are about equal,the air velocity is so low that the suction air stream cannot carry all:oi the oxide and it will settle in the pipe.

The principal object of this invent-ion, therefore, is to provide yanimproved turnace of the above type which is operable to produce moreoxide of higher purity.

A further object of this invention is to provide a furnace of the abovetype with means for independently regulating the rate of air ilow sateach hearth section without :affecting the fair ilow at .any otherhearth section so that optimum conditions can be obtained at all ol thehearth sections.

Another object of this invention is to provide a furnace of the abovetype with an individual exhaust tube lior each hearth section, andadnaft or suction tube which is connected to the majority of the exhausttubes at a position such `that these exhaust tubes are `all ofsubstantially the same length.

if' 21,958,588 C@ Patented Nov. 1, 1960 AFurther objects, features andadvantages of this invention Will be come apparent from a considerationof the iollowing description, the appended claims and the accompanyingdrawing in which:

Figure 1 is a fragmentary vertical sectional View of the furnace of thisinvention;

Fig. 2 is an enlarged fragmentary sectional view looking along the line2-2 in Fig. 1;

Fig. 3 is a plan view oi the turnace of this iuvention, with some partsbroken away and other parts shown in section for the purpose of clarity;

Fig. 4 is an enlarged transverse sectional view looking along the line 44 in Fig. 3;

Fig. 5 is a sectional view looking along the line 5--5 in Fig. 3;

Fig. 6 is a horizontal sectional view of the distributor box in thefurnace of this invention;

Fig. 7 is a sectional view looking along the line 7-7 in Fig. 4; and

Fig. 8 is a `fragmentary sectional view looking along the line 8 8 inFig. 3.

With reference to the drawing, the furnace of this invention, indicatedgenerally :at 10, is illustrated in Fig. 1 as including a main fname 12which supports an annular hood or furnace shell 14 at a position .abovea supporting door surface 16. The hood 14 has tubular inner and outerwalls 18 and 20 arranged in a concentric relation and connected by a topwall 22 .of substantially annular shape.

An annular hearth 24, of substantially trough-shape in transversesection, is located Within th-e lower portion of the hood `14. As shownin Fig. 2, the width of the hearth 24 is less than the width of the hood14 so that spaces 26 and 28 lare provided between the hearth and theinner and outer hood wallslS and 20, respectively. The hearth 24 ismounted on a supporting I-beam 30 which is in turn carried on a ringgear 32 rotatably driven by any suitable means and supported on rollersA pair of spaced partitions 23 and 25, which extend substantiallyradially of the hood 14, project upwardly from positions adjacent thetop side of the hearth 24 so las t-o divide the furnace into a smallfeeding zone 27 and an elongated heating zone 29 which extends from thepartition 25 in a counterclockwise direction, as viewed in Fig. 3, tothe partition 23.

Bel-ow its top wall 22, the hood 14 is provided with a refractory arch36 which extends the complete length of the heating zone 29 and formsthe top wall of a heating chamber `40 disposed between the hearth member24 and the arch 36. A plurality of heating elements 42 extendsubstantially radially of the hood 14 through the chamber 40 and arepositioned adjacent their ends in refractory blocks 44 supported onplates 46 carried by the inner and outer side walls 18 and 20 of thehood 14. Each heating element 42 is of the silicon carbide elec tricalresistance type such as the Globar elements man-ufactured by theCarborundum Company :and is supported at lits ends by metal clips (notsho-wn) which are supported on the furnace main frame and function asthe electrical contacts for the heating elements.

At substantially equally spaced locations Iin the heat ing zone 29,hollow exhaust port members 48 :are supported on the outer plate 46.Each member 48 is positioned between two groups of heat-ing elements 42and extends from `a point above the hearth to the outer side wall 20 ofthe hood 14. At the wall 20, each port member 48 communicates with thehorizontal portion 50 of an exhaust tube 52 which extends upwardly fromthe hood 14. At its upper end, each tube 52 is connected to a downwardlyextending pipe 54 ou :a distributor box 58 3 located labove the hood 14so that its conicides with the vertical Iaxis 56 of lrotation of thehearth 24.

Since the hearth 24 is rotated in a counterclocltwise direction asviewed in Fig. 3, the exhaust tubes 52 are provided with consecutiveletter sux designations irom V1l-41, inclusive also in acounterclockwise direction about the hearth, to facilitate referencehereinafter to individual tubes. All of the exhaust tubes 52c-n,inclusive, are of substantially the same length and are connected by thepipes 54 to the distributor box 58 which forms a part of an upwardlyextending draxft tube connected to any suitable fan or other suctionmeans for exerting substantial upward drafts in the tubes 52c-n. The box58 has a cone shape bottom 59 to facilitate a smooth upward iiow ofvolatilized oxide from the tubes 52.

As shown in Fig. 4, each exhaust tube 52 has a damper assembly 6udisposed in a vertical portion 62 thereof adjacent the horizontalportion 50. Each damper assembly 60 includes a plate 64 mounted formovement about a horizontal shaft 66 to diiferent adjusted positions.Each damper assembly 60 is operable to control the ,amount of air andvolatilized oxide which flows upwardly in the tube 52 in which the.assembly 60 is installed. l 'De maintain the porthole members 48 clearof solidii'ied oxide, a porthole cleaning mechanism 70 is mountedadjacent each porthole member 48. Each mechanism 70 is mounted on asupporting bracket 72 secured to the outer wall 20 of the hood 14, andincludes a pneumatic piston :and cylinder assembly 74 consisting of ahorizontal cylinder 76 secured to the bracket 72 and a piston rod 78which extends from the cylinder 76 toward the porthole member v48. Onits terminal end, the piston -rod 78 carries ya circular plate 80located within the horizontal portion 50 of the adjacent tube 52 andprovided with pointed blades 82. The piston rod 78 extends through anopening in a vertical back door 84, for the exhaust tube portion 50,which can be opened for manual cleaning of the portion 50 andmaintenance of the mecha- On operation of the cylinder assembly 74 toextend the piston rod 78, which is shown in its retracted position inFig. 4, the plate 80 is moved to a position adjacent to but slightlyinwardly of the inner end 85 o the exhaust port member 48. 4In thisposition of the plate 80 the blades 82 project out of the member 48 sothat substantially :all of the solidified oxide in the member 48 hasbeen pushed back onto the hearth 24 to maintain the passage 86 throughthe member 48 clear for the travel of gaseous products therethrough.

1n the use of the furnace 10, the hearth 24 is filled with sand 88, andtechnical -gnade oxide, which is in powder form, is red from storagebins to the upper end of :a feed hopper 90 located yabove the lhearth inthe feeding zone 27. As shown in Figs. and `8, the zone 27 has a topwall 91 supported on horizontal beams 93 which are 1a part of the mainframe 12. The oxide in the hopper 90 is discharged iirom the l-ower end94 thereof by a ffeed roll 98 which is driven by a motor 116 and extendsradially across the hearth 24. The roll 98 is Igenerally cylindrical inshape and has grooves 99 in its outer surface. On rotation oi the roll98, each groove 99 fills with oxide in the hopper 90 .and then depositsthis oxide onto the upper end of an inclined ifeed plate 100 positionedbelow the hopper 90. The [feed plate 100 is suspended from the yframe 12by rods 101 'and is fonmed with small downwardly extending grooves 2which maintain the yform of the oxide issuing from the feed roll 98 as awide ystream and deposit the oxide on the hearth 24. This bed of oxidethen travels with the rotating hearth 24 in a counterclockwise directionas viewed in Fig. 3 so that after it travels under the partition 25 itis exposed to the heat trom the heating elements 42. The heat in thechamber 40 quickly brings the temperature orf the oxide to avolatil-izing temperature.

The oxide bed on the hearth 24 which is in a position opposite the iirstexhaust tube, indicated at 52a in Fig. l, is in a heated condition suchthat some volatilized oxide is present. This volatilized oxide is drawnupwardly through the exhaust tube 52a which communicates with l.a drafttube 104 which is also connected to the draft tube 52b opposite the nextporthole member 48. The draft tube 104 also communicates with an exhaustduct 106 which terminates at its lower end in the feeding `zone 27 sothat any dust in the zone 27 is drawn upwardly through the duct 106 tothe draft tube 104 where it is mixed with the oxide :fumes drawnupwardly through the exhaust tubes 52a and 52b. In the draft tube 104the temperature of the oxide and is lowered to about 180200 F. and theresulting solid or crystalline oxide is conveyed by the air to asecondary baghouse where it is tied into a conveyor mechanism whichterminates in an upright feeder tube 105 (Figs. 3 and 5) located in thefeeding zone 27. The tube 105 deposits this oxide, which is of a lowerpurity than desired, onto the hearth 24 for travel into the heating zone29. Removal of the 4dust from the feeding zone 27 through the duct 106prevents any of the dust from being drawn into the heating zone 29 andadversely adecting the purity of the volatilized oxide therein.

The oxide bed on the hearth 24 opposite the third exhaust tube 52C is inthe desired sticky state. Consequently, the vol'at-illized oxidewithdrawn Itrom the hearth through the exhaust tube 52e is of a higherquality than that Withdrawn through the tubes 52a and 52b. This qualityis maintained by adjusting the damper assembly 60 for the tube 52e sothat optimum conditions are maintained on the oxide bed on the sectionof the hearth 24 adjacent the exhaust tube 52e. By virtue of theconnection of all of the exhaust tubes 5'2c-n to the draft tube 58 at fasingle point, an adjustment of the damper assembly 60 for the tube 52eis divided between all of the other exhaust tubes so that the amount ofexhaust air at any one hearth section is not affected to any greatextent. In other words, if the damper assembly 60 ior the tube 52C isadjusted to decrease the exhaust through the tube 52e, the correspondingtotal exhaust increase for the other tubes 52d-n is equally dividedbetween the tubes so that the effect on any one tube is minimized. Theadjustment of the damper assembly 60 controls the amount of which iiowsupwandly through the space 26 opposite the tube 52e so that the inner ofthe hearth is cooled and the volume of air traveling across the hearth24 is sufiicient to maintain the oxide bed in the desired state. alsotravels upwardly through the space 28 adjacent the exhaust tube 452Cprimarily rfor cooling the outer rim of the hearth. The amount of airwhich travels upwardly through the space 28 corresponding to each tube52 is controlled by a pair of dampers 1'12 `and 113 of manually4adjustable type carried by the hood 14. Each damper 112 is located inthe outer wall 20 adjacent the lower end off the space 28, and eachdamper 113 is located in a wall which closes the lower end of the space28.

Adjustment of the dampers 112 and/ or 113 is effective to control theratio of air admitted to the inner side of the corresponding hearthsection to the air admitted to the outer side of the hearth section. Therestriction of the amount of air permitted to enter the space 28 insuresan upward travel of air through the space 26, so that air sweeps acrossthe hearth in sufficient quantity to convey the sublimed oxide into theporthole members 48. By adjusting a corresponding pair of dampers 64 and112 o r 113, the air at the sides of the corresponding hearth section isregulated so that the inner and outer sides of the M003 bed on thehearth are cooled and solidify so that they form barriers to prevent anyliquid portions of the bed from running olf the hearth, and the desiredvolume of air is provided for sweeping the sublimed M003 from thehearth. Any spillage of oxide oi the bed is noticeable at the dampers113 and either or both dampers `'112 and .113 are adjusted at eachhearth section to provide the `primary baghonse for collection andsubsequent densifying and packaging.

The residue remaining on the hearth after a complete revolution of thehearth is removed by` a `tailing screw 114 (Fig. 5) which extendstransversely of the hearth 24 in the feeding zone 27 at a positionbetween the partition 23 and the feed roll 98. As a result of thecontinuous operation of the screw 114, all of the residue on eachportion of the hearth is removed before additional oxide is depositedthereon by the feed roll 98. The dust resulting from operation of thescrew 114 is removed from the zone 27 by the duct 106. A chain 115extends about sprockets i117 and 119 on the tailing screw 114 and thefeed roll 98, respectively, to provide for driving of the screw 114 bythe motor 116. The residue removed from the hearth by the tailing screw114 falls from the screw into a hopper 120 located below one end of thescrew. This residue is equal to about 30-40% of the original oxidecharge.

The porthole cleaning mechanisms 70 are operated automatically by anysuitable control mechanism so that each cylinder assembly 74 is operatedat predetermined intervals of time to extend the piston rod 78 so thatthe disk 80 and blades 82 maintain the porthole passage 86 free of solidoxide which would interfere with the air flow across the correspondinghearth section.

It will be understood that the specific construction of the improvedsublimed oxide furnace herein disclosed and described is presented forpurposes of explanation and illustration, and is not intended toindicate limits of the invention, the scope of which is defined by thefollowing claims.

What is claimed is:

l. In a furnace for producing high purity M003 from lower purity M003which includes a horizontal annular hearth mounted for rotation about asubstantially vertical axis, means operatively associated with thefurnace for feeding M003 onto said hearth, a hood arranged in a coveringrelation with said hearth, and heating means above the hearth forvolatilizing M003 thereon; a plurality of exhaust tubes connected toperipherally spaced portions of the hood at positions adjacent saidhearth for withdrawing said volatilized M003 therefrom, draft tube meansconnected to said exhaust tubes at a single point remote from said hoodfor providing drafts therein for withdrawing said volatilized M003 fromsaid furnace, means for supplying air to said hearth, and meansoperatively associated with each of said exhaust tubes for regulatingand adjusting the rate of flow of material therein.

2. In a furnace for producing high purity M003 from lower purity M003,said furnace including a horizontal annular hearth mounted for rotationin one direction about a substantially vertical axis, means for feedingsaid lower purity M003 to one portion of said hearth, an annular hoodhaving horizontally spaced inner and outer side walls which extenddownwardly to positions horizontally spaced from the inner and outersides, respectively, of the hearth so as to provide spaces for theupward travel of air on the inner and outer sides of the said hearth,heating means in the hood above the hearth, hollow exhaust port membersmounted on peripherally spaced portions of said hood at positions abovesaid hearth, each of said port members extending horizontally from apoint above the hearth to the outer side wall of said hood, theimprovement comprising a plurality of exhaust tubes corresponding tosaid exhaust port members, each one of the majority of said exhausttubes communicating with the corresponding exhaust port member andextending upwardly therefrom to a single point above said hood, a drafttube connected to the upper ends of the exhaust tubes at said singlepoint for providing `upwardly traveling drafts therein, the remainingones of said exhaust tubes being located adjacent said feeding means onthe side thereof in the direction of rotation of said hearth, separatedraft means connected to said remaining exhaust tubes, and separatedamper means in .each of said exhaust tubes for adjusting the drafttherein to obtain optimum draft conditions at the hearth sectioncorresponding thereto.

3. In a furnace for producing high purity M003 from lower purity M003which includes a horizontal annular hearth mounted for rotation about asubstantially vertical axis and having an inner side and an outer side,means operatively associated with the furnace for feeding M003 onto saidhearth, an annular hood arranged in a covering relation with said hearthand spaced from said sides, and heating means above the hearth forvolatilizing M003 thereon; a plurality of exhaust tubes connected toperipherally spaced portions of the hood at positions adjacent saidhearth for withdrawing said volatilized M003 therefrom, draft tube meansconnected to said exhaust tubes lat a single point remote from said hoodfor providing drafts therein for withdrawing said volatilized M003 fromsaid furnace and for drawing air into said furnace through the spacesbetween said hearth sides and said hood, and individually adjustabledamper means in each of said exhaust tubes.

4. In a furnace for producing high purity M003 from lower purity M003,said furnace including a horizontal annular hearth mounted for rotationin one direction about a substantially vertical axis, means for feedingsaid lower purity VM003 to one portion of said hearth, an annular hoodhaving horizontally spaced inner and outer side walls which extenddownwardly to positions horizontally spaced from the inner and outersides, respectively, of the hearth so as toprovide spaces for the upwardtravel of air 0n the inner and outer sides of said hearth', and heatingmeans in the hood above the hearth; a plurality of exhaust tubes mountedon peripherally spaced portions of said hood, the majority of saidexhaust tubes being of substantially the same 'length and extendingupwardly from said hood to a single point above the hood, a draft tubeconnected to the upper ends of the exhaust tubes at said point forproviding upwardly traveling drafts therein, and separate damper meansin each of said exhaust tubes for adjusting the draft therein to obtain`optimum draft condtions at the hearth section corresponding thereto.

5. In a furnace for producing high purity M003 from lower purity M003which includes a horizontal annular hearth mounted for rotation about asubstantially Vertical axis and having an inner side and an outer side,means operatively associated with the furnace for feeding M003 onto saidhearth, an annular hood arranged in a covering relation with said hearthand spaced from said sides, and heating means above the hearth forvolatilizing M003 thereon; a plurality of exhaust tubes connected toperipherally spaced portions of the hood at positions adjacent saidhearth for withdrawing said volatilized M003 therefrom, draft tube meansconnected to said exhaust tubes vat a single point remote from said hoodfor providing drafts therein for withdrawing said volatilized M003 fromsaid furnace and for drawing air into said furnace through the spacesbetween said hearth sides and said hood, individually adju-stabledamperl means on said hood for controlling the air admitted to the outerside of said hearth for thereby controlling the ratio of the amounts ofair admitted to the inner and outer sides of lower purity M003, saidfurnace including a horizontal annular hearth mounted for rotation inone direction 'about a substantially vertical axis, a hood positionedover said hearth and having horizontally spaced inner and outer sidewalls which extend downwardly to positions on opposite sides of thehearth, partition means in the hood extending downwardly to a positionadjacent the hearth and dividing the interior of the hood into a feedingsection and a heating section, means for feeding M003 onto the hearth insaid feeding section, said heating seo tion having an inlet end and anoutlet end, and heating means in said heating section for continuouslyheating M003 traveling 011 said hearth from said inlet end to saidoutlet end; the improvement comprising providing means for admitting airto the portion of said hearth in said heating section, exhaust tubemembers mounted on and communicating with the interior of said hood atsubstantially equally spaced positions in said heating section, a drafttube connected to the majority of said exhaust tubes at a single pointllocated such that said majority are all of substantially the samelength, and adjustable means on said exhaust tubes for -regulating theflow of material therethrough.

7. In a furnace for producing high purity M003 from lower purity M003,said furnace including a horizontal annular hearth mounted for rotationin one direction about a substantially vertical axis, a hood positionedover said hearth and having horizontally spaced inner and outer sidewalls which extend downwardly to positions on opposite sides of thehearth, partition means in the hood extending downwardly to a positionadjacent the hearth and dividing the interior of the hood into a feedingsection and a heating section, means for feeding M003 onto the hearth insaid feeding section, said heating section having an inlet end and anoutlet end, and heating means in said heating section for continuouslyheating M003 traveling on said hearth from said inlet end to said outletend; the improvement comprising providing means for admitting air to theportion of the said hearth in said heating section, exhaust tube membersmounted on and communicating with the interior of said hood atsubstantially equally spaced positions in said heating section, firstdraft tube means connected to some of said exhaust tubes adjacent saidinlet end, means communicating said first draft tube means with saidfeeding section for removing dust therefrom, second draft tube meansconnected. tothe remainder of said exhaust tubes at a single pointlocated such that said remainder are all ofV substantially the samelength, and adjustable means on said exhaust tubes for regulatnig theflow of material therethrough.

8. In a furnace for producing high purity M003 from lower purity M003,said furnace including a horizontal annular hearth mounted for rotationin `one direction about a substantially vertical axis, means for feedingsaid lower purity M003 to one portion of said hearth, an annular hoodhaving horizontally spaced inner and outer side walls which extenddownwardly to positions horizontally spaced from the inner and outersides, respectively, of the hearth so as to provide spaces for theupward travel of air on the inner and outer sides of the said hearth,heating means in the hood above the hearth, hollow exhaust port membersmounted on peripherally spaced portions of said hood at positions abovesaid hearth, each of said port members extending horizontally from apoint above the hearth to the outer side wall of said hood; theimprovement comprising a plurality of exhaust tubes corresponding tosaid exhaust port members, each one of the majority of said exhausttubes communicating with the corresponding exhaust port member andextending upwardly therefrom to a single point above said hood, a drafttube connected to the upper ends of the exhaust tubes at said singlepoint for providing upwardly traveling drafts therein, the remainingones of said exhaust tubes being located adjacent said feeding means onthe side thereof in the direction of rotation of said hearth, separatedraft means connected to said remaining exhaust tubes, adjustable dampermeans for control-ling the amount of air admitted to the space on theouter side of said hearth and thereby controlling the ratio of theamounts of air admitted to the inner and outer sides of said hearth, andseparate damper means in each of said exhaust tubes for adjusting thedraft therein to obtain optimum draft conditions at the hearth sectioncorresponding thereto.

References Cited in the le of this patent UNITED STATES PATENTS

1. IN A FURNACE FOR PRODUCING HIGH PURITY M0O3 FROM LOWER PURITY MOO3WHICH INCLUDES A HORIZONTAL ANNULAR HEARTH MOUNTED FOR ROTATION ABOUT ASUBSTANTIALLY VERTICAL AXIS, MEANS OPERATIVELY ASSOCIATED WITH THEFURNACE OF FEEDING MOO3 ONTO SAID HEARTH, A HOOD ARRANGED IN A COVERINGRELATION WITH SAID HEARTH, AND HEATING MEANS ABOVE THE HEARTH FORVIOLATION MOO3 THEREON, A PLUARITY OF EXHAUST TUBES CONNECTED TOPERIPHERALLY SPACED PORTIONS OF THE HOOD AT POSITIONS ADJACENT SAIDHEARTH FOR WITHDRAWING SAID VOLATILIZED MOO3 THEREFORM DRAFT TUBE MEANSCONNECTED TO SAID EXHAUST TUBES AT A SINGLE POINT REMOTE FROM SAID HOODFOR PROVIDING DRAFTS THEREIN FOR WITHDRAWING SAID VOLATILIZED MOO3 FROMSAID FURNACE MEANS FOR SUPPLYING AIR TO SAID HEARTH, AND MEANSOPERATIVELY ASSOCIATED WITH EACH OF SAID EXHAUST TUBES FOR REGULATINGAND ADJUSTING THE RATE OF FLOW OF MATERIAL THEREIN.